Microcapsules as carriers for color reaction components in color reaction paper and process of making said microcapsules

ABSTRACT

Process of making microcapsules as carriers for encapsulated solid or liquid color components in color reaction papers, wherein particles of finely divided solid substances are incorporated in the capsule walls during the formation of the capsules by chemical reaction from a film forming component dissolved in the dispersed phase of a liquid dispersion system, which contains dissolved in its continuous phase a low-molecular weight reactant for the film-forming component; also contained in the dispersion system are said solid particles to be incorporated into the walls of the microcapsules. Very high percentages of solid particles, i.e., considerably higher than 100 percent calculated on the weight of the capsule wall, can thus be incorporated into the latter thereby increasing the resistance of the walls to mechanical stress far above the limit of known microcapsules.

O United States Patent [151 3,639,257

Harbort 1 Feb. 1, 1972 [54] MICROCAPSULES AS CARRIERS FOR [56]References Cited COLOR REACTION COMPONENTS IN UNITED STATES PATENTSCOLOR REACTION PAPER AND 3,016,308 1/1962 Macaulay ..252/3l6 x PROCESSOF MAKING SAID 3,044,289 6/1962 Katchen et al... .....252/3l6MICROCAPSULES 3,137,630 6/1964 Heckcr et al. ..264/|4 3,l79,600 4/l965Brockett ..252/3 16 X [72] Inventor: Ludwig IIarbort, Hannover, GermanyPrimary ExaminerRichard D. Lovering [73] Assignee. Gunther Wagner PehkanWerke, Han Atmmey McGlew and Tom nover, Germany [22] Filed: June 24,I968 [57] ABSTRACT [21] A L N 739,363 Process of making microcapsules ascarriers for encapsulated solid or liquid color components in colorreaction papers, wherein particles of finely divided solid substancesare incor porated in the capsule walls during the formation of the cap-[30] Foreign Application Priority Data sules by chemical reaction from afilm forming component dissolved in the dispersed phase of a liquiddispersion system, june 23, 1967 Germany ..W 44228 which containsdissoved in its continuous Phase a low une 24, 1967 Germany ..W 44240molecular weight reactant for the fi|m forming component; also containedin the dispersion system are said solid particles [52] US. Cl...252/3l6, 106/308 C, 117/362, 10 b incorporated i the walls of themicrocapsules. Very 117/ 100 A, ll7/l00 B, 162/162, 264/4 highpercentages of solid particles, i.e., considerably higher [51] Int. Cl..1301] 13/02, 844d 1/02 than 100 percent calculated on the weight of thecapsule wall, [58] Field of Search ,252/316; 424/35; 1 17/1 10 A, canthus be incorporated into the latter thereby increasing the 1 1 00 3 32; 2 4 resistance of the walls to mechanical stress far above the limitof known microcapsules.

2 Claims, 1 Drawing Figure I v: hr 0 t mm fl, il 5, wi l 1531/55?fZi'J'iY/ZZ ill)!!! 0/ talour 101 111/011 (only, film Inn A I finelydiv/Id Jul/d sumo/m) 0 (Mill/Jill? 0/ 8 /'/I l) d/itg/am. rum, g 0/Milli/id drop/e! l/qram rum. nfrapnlu a. flu 121 y ton/g1! MICROCAPSULESAS CARRIERS FOR COLOR REACTION COMPONENTS IN COLOR REACTION PAPER ANDPROCESS OF MAKING SAID MICROCAPSULES SUMMARY OF THE INVENTION Thepresent invention relates to miniature or microcapsules as carriers forcolor components in color reaction papers and a process of making saidmicrocapsules. The invention further includes a method for preparingcolor reaction paper with the microcapsules-containing materials madeaccording to the invention.

In duplicating papers making use of the color reaction process it hasrecently become known to use microcapsules in which color components areenclosed. These processes have the advantage that no undesirablereaction between colorproducing substances can take place duringhandling and storage.

Difficulties are however encountered in the preparation of the papers,since the microcapsules are very sensitive to mechanical stress becausethe walls of the capsules are very thin. Special precautionary measuresare therefore necessary during the incorporation into the coatingcomposition of the paper or the paper pulp in order to avoid damage tothe capsules.

Several attempts have been made to overcome the above difficulties, oneof which consists in making double walled capsules; this, however, isnot a satisfactory solution of the problem, because it involvesadditional operations in the processing and consequently raises thecosts; moreover, it was found that the microcapsules so produced are notsatisfactory for practical purposes in every respect.

In another process previously developed by the same inventor,microcapsules were produced enclosing liquid or solid substances, byproducing an insoluble reaction product from a film-forming componentdissolved in the dispersed phase of a liquid dispersion system, whichalso contains, in its continuous phase, a low-molecular weightsubstance; the reaction of the two dissolved substances results in saidinsoluble capsuleforming product. In this case, too, the capsules arethin walled and present the same difficulties in handling as aboveexplained.

It is an object of the present invention to overcome the disadvantage ofthe weakness of the walls of the microcapsules and to providemicrocapsules of sufficient strength and stability and for being used inthe production of color reaction papers without any precautionarymeasures being necessary.

It is another object of the invention to provide a process for makingsuch microcapsules.

It is yet another object to provide color reaction papers with themicrocapsules-containing materials made according to the invention.

Other objects and advantages of the invention will become apparent fromthe following detailed description.

It was found that according to the invention the objects are realizedwhen in further development of the process for making microcapsules bychemical reaction, from a liquid dispersion, of a polymeric product bythe reaction of two components dissolved in the dispersed and thecontinuous phases of said liquid system, respectively, particles offinely divided solid substances are incorporated into the walls of thecapsules under formation.

It was also found that for practical purposes it is very advantageous touse as chemical reaction the saponification of a cellulose ester of anorganic acid or the denitration of cellulose nitrate, which is dissolvedin the dispersed liquid phase, by a low-molecular substance dissolved inthe continuous phase, for instance by alkali metal hydroxide or sodiumhydrogen sulfide, the reaction resulting in a product insoluble in boththe dispersed and the liquid phases. While this reaction occurs, thefinely divided solid substances which are suspended in the dispersedphase are to a substantial extent built into the walls of themicrocapsules, thus increasing the strength thereof so as to positivelyexclude damages to the microcapsules during their incorporation intopaper pump or paper-coating materials.

The finely divided solid substances can be of various types. For theproduction of duplicating papers with color reaction components,primarily colorless or white solid substances should be chosen.

It has been found that the stability of the microcapsules according tothe process of this invention will generally be increasedp'roportionately with the contents of solid substances in the walls ofthe capsules. It is thus possible, substantially to graduate thestability and the strength properties of the microcapsules and to adaptthem to the actual purpose for which they are used. It is possible toincorporate in the walls of the capsules up to 750 percent by weight offinely divided solid substances, calculated on the weight of the capsulewalls. The process has a further advantage: by using white pigments withhigh-covering power, for example, zinc sulphide and titanium dioxide, itis possible to obtain microcapsules which, because of their opticalreflection properties, also permit the use of color components ofrelatively strong natural coloring for colorless duplicating papers;hitherto such colorants could not be considered for this purpose.

If the low-molecular weight substance dissolved in the continuous phaseis allowed to act on the dispersed phase containing the cellulose esterand the finely divided solid substance until the entire cellulose esteris converted into the polymeric reaction product, then the solidsubstance finely divided in the dispersed phase is completely depositedin the capsule wall which will then consist of the polymerlike reactionproduct, and particularly thick walled capsules are obtained envelopinga liquid core. If the reaction is prematurely stopped, capsules areobtained which have thinner walls and whose walls contain only a part ofthe solid substance finely dispersed in the dispersed phase. Theresidual portion of the solid substance remains dispersed in the liquidcore of the capsules, in which a corresponding portion of unreactedfilm-forming substance is dissolved.

As already mentioned, one of the advantages of this process, as comparedto other capsule-forming processes in which likewise solid substancescan be incorporated into the capsule wall, consists in that far greaterquantities of finely divided solid substances can be transferred intothe capsule wall. By this means, capsules are obtained which show adecidedly better stability with respect to mechanical stress. Inaccordance with the process more fully described below, it is possibleto incorporate very high percentages by weight of different finelydivided solid substances into the capsule wall, i.e., considerably morethan percent, calculated on the weight of the capsule wall. When usingsolid particles having high covering power, as for example titaniumdioxide or carbon black, it is possible to obtain capsules by thisprocess which are impervious to light, so that the colored contents ofthe capsules are substantially hidden and light sensitive substances canbe encapsulated, whereby new possibilities of using encapsulatedsubstances can be obtained.

In the following examples the invention will be described in full detailbut it should be understood that the examples are only given by way ofillustration and not of limitation and many changes and modifications inthe details can be made without departing from the spirit of theinvention.

All parts are by weight where not otherwise indicated.

EXAMPLE I Dispersed Phase Solution of 3-methyl spiro-dinaphthopyran andcellulose acetobutyrate, the latter as film fonner in a mixture ofcyclohexanone and diphenoxyethyl formal, in which titanium dioxide issuspended. Continuous phase Solution of sodium hydroxide in water.

34 parts of cellulose acetobutyrate (acetyl content 13 percent, butyrylcontent 37 percent) are dissolved together with 1 part of 3-methylspiro-dinaphthopyran in a mixture of 40 parts of cyclohexanone and 25parts of diphenoxyethyl formal and 6.8 parts of finely divided titaniumdioxide are suspended in this solution. The suspension is heated to 80C., it is dispersed in 330 parts of a 9 percent aqueous sodium chloridesolution which is heated to 80 C.* (*The so obtained emulsion is pouredwhile stirring into 275 parts of weight of aqueous 18 percent sodiumhydroxide solution, which is heated to 70 C.) After a reaction period of15 minutes, all of the cellulose acetobutyrate, which had been presentin the droplets of the emulsion is converted into cellulose, andcapsules have been formed whose walls, consisting of cellulose, containincorporated therein all of the titanium dioxide which had been present.The ratio of weight in the walls is therefore 40 percent of titaniumdioxide, since in the saponification of the cellulose acetobutyrate 50percent of cellulose are produced. The capsules which have a size of to30p are washed with water. Thereby, the cyclohexanone is removed fromthe contents of the capsules and there remains the solution of the colorforming compound in diphenoxyethyl formal. The capsules have a goodstability. They can be used for the production of color reaction papers.

EXAMPLE I] 20 parts of finely divided zinc sulphide are suspended in asolution of 1 part of color forming compounds and 25 parts of celluloseacetobutyrate (13 percent acetyl, 37 percent butyryl), in a mixture of49 parts of cyclohexanone and 25 parts of liquid chlorinated paraffin.The suspension is heated to 80 C. and dispersed in 390 parts of a 9percent aqueous sodium chloride solution, whereafter the emulsionobtained is incorporated by stirring into 353 parts of an 18 percentsolution of sodium hydroxide in water. After a reaction time of minutesat 70 C., the entire quantity of cellulose acetobutyrate, which had beenpresent in the droplets of the emulsion, is converted into cellulose andthe entire quantity of zinc sulphide becomes part of the walls of thecapsules formed from the cellulose. Consequently, 160 percent of zincsulphide calculated on the weight of cellulose have been incorporatedtherein. The size of the capsules is 5-20p.. Owing to their high contentof solid particles, they are even more stable than the capsules obtainedaccording to example 1.

EXAMPLE Ill parts of finely divided zinc sulphide are suspended in asolution of 1 part of Ceres blue and 34 parts of cellulose acetobutyrate(acetyl content 13 percent, butyryl content 37 percent) in a mixture of40 parts of cyclohexanone and parts of diphenoxyethyl formal. Thesuspension is heated to 50 C. and dispersed in 216 parts of a 16.7percent aqueous sodium chloride solution, whereafter the emulsionobtained is incorporated by stirring into 420 parts of 14.3 percentsodium hydroxide solution. After a reaction time of 15 minutes at 70 C.,all the cellulose acetobutyrate is converted into cellulose and theentire zinc sulphide is transferred into the capsule wall, which meansthat 118 percent of zinc sulphide, calculated on the weight of thecapsule wall, are incorporated therein. The size of the capsules isbetween 10 and 801.1,. They show a pale blue color, whereas capsulesprepared in accordance with the same specification without zinc sulphideshow a color similar to deep blue ink. A distinct covering effect isthus caused by the strong pigmentation of the capsule wall.

EXAMPLE IV 1 part of Ceres blue was dissolved together with parts ofcellulose propionate in a mixture of 44 parts of cyclohexanone and 25parts of diphenoxyethyl formal and 20 parts of titanium dioxide weresuspended in this solution. The suspension was heated to 85 C. anddispersed in 198 parts of 9 percent reaction time of 15 minutes at 70C., capsules were obtained,

and all the titanium dioxide was incorporated into the walls of thecapsules, which consist of cellulose, based on the weight of the capsulewall, the amount of titanium dioxide is 67 percent. The size of thecapsules is approximately 2040p.. Differing from capsules consisting ofcellulose, which contain no titanium dioxide in the capsule wall andappear to be of a deep blue, the capsules made according to this exampleare pale blue.

EXAMPLE V 1 part of Ceres blue was dissolved togetherwith 24 parts ofcellulose acetate in a mixture of 50 parts of cyclohexanone and 25 partsof diphenoxyethyl formal; 20 parts of titanium dioxide were suspended inthis solution. The suspension was heated to C. and dispersed in 198parts of 9 percent aqueous sodium chloride solution, whereafter theemulsion obtained was incorporated by stirring into 420 parts of 14.3percent sodium hydroxide solution. Capsules were obtained after areaction time of 15 minutes at 70 C., in whose walls, consisting ofcellulose, all the titanium dioxide is incorporated, this amounting to166 percent of titanium dioxide, based on the weight of the capsulewall. The size of the capsules is between 1 and 40 u. They are pale bluein color.

According to the process indicated in examples I to V, it is possible toincorporate other finely divided solid substances into the capsule wall,and in fact calcium carbonate, a mixture of titanium dioxide and zincsulphide 1:1.5, tertiary calcium phosphate, a mixture of titaniumdioxide and calcium carbonate 1:2.4, and also barium sulphate and zincoxide may be so incorporated. In all these cases, by incorporation ofthe solid substances into the capsule wall, an increase in the stabilityof the capsules is produced, this increase being more pronounced as thequantity of incorporated solid substance becomes larger. It isaccordingly possible for the stability of the capsules to be graduatedas required and they may be adapted to the actual purpose for which thecapsules are being used.

Another possibility of producing capsules consists in the conversion ofcellulose nitrate by denitration, whereby products are obtained whichare very similar to cellulose. As shown by the following examples inthis case, it is likewise possible to incorporate large quantities offinely divided solid substances in the capsule walls to obtain aconsiderable improvement in the stability of the capsules as well as inoptical important properties thereof.

EXAMPLE V1 0.5 part of titanium dioxide is suspended in 10 parts of asolution of 1.2 parts of cellulose nitrate (N-content 10.92 percent), ina mixture of 6.2 parts of cyclohexanone and 2.5 parts of diphenoxyethylformal. The suspension is heated to C. and it is emulsified in 50 partsof a 20 percent solution of sodium chloride in water at 75 C. Aftercooling to 60 C., 50 parts by volume of a 14 percent solution of sodiumhydrogen sulphide in water are added to the emulsion and the mixture ismaintained at 40 C. while stirring for 1 hour.

After this time, all the cellulose nitrate which had been present in thedroplets of the emulsion is denitrated and the capsules thereby formedcontain in their wall all the titanium dioxide, corresponding to 66percent, based on the weight of the capsule wall.

The capsules are washed with water. They are considerably more stablethan capsules of the same type and size which do not contain anytitanium dioxide in their wall. The size of the capsules is 30 to 50 u.

EXAMPLE Vll 1.44 parts of titanium dioxide are suspended in 15 parts ofa solution of 1.2 parts of cellulose nitrate (N-content 10.92

percent) and 0.1 percent of Ceres blue in a mixture of 6.2 parts ofcyclohexanone and 2.5 parts of diphenoxyethyl formal. The suspension isheated to 100 C. and it is emulsified in 75 parts of a 20 percent sodiumchloride solution in water at 75 C. After cooling to 60 C., 75 parts byvolume ofa 14 percent solution of sodium hydrogen sulphide in water areadded to the emulsion and the mixture is maintained at 40 C. whilestirring for 1 hour. After this time, all the cellulose nitrate in thedroplets is denitrated and the capsules which have formed contain intheir wall the entire quantity of titanium dioxide, corresponding to 127percent, based on the weight of the capsule wall. The capsules arewashed with water and separated out; they are only pale blue in color,because of the high titanium dioxide content in the capsule wall;without titanium dioxide in the capsule wall, they are deep blue. Thesize of the capsules is between 20 and 40 u.

EXAMPLE Vlll 1.03 parts of carbon black are suspended and finelydispersed in 15 g. of a solution of 1.2 parts of cellulose nitrate(N-content 10.92 percent) in a mixture of 6.3 parts of cyclohexanone and2.5 parts of diphenoxyethyl formal. The suspension is heated to 70 C.and it is emulsified in 70 parts of a percent sodium chloride solutionin water at 70 C. After cooling to 50 C., 73 parts by volume of a 14percent solution of sodium hydrogen sulphide in water are added to theemulsion and the mixture is maintained for 45 minutes at 40 C. whilestirring steadily. After this time, all the cellulose nitrate isdenitrated and the capsules which have formed contain in their wall allthe carbon black, corresponding to 91 percent, based on the weight ofthe capsule wall. The capsules are black and very stable; their size ison average about t.

Similarly to example Vlll, any desired smaller quantities than 91percent of carbon black can be incorporated into the capsule wall,whereby the possibility is provided of a graduation of the stability andoptical properties of the capsules in this case, too.

EXAMPLE [X 0.7 parts by weight of Milori blue (pigment content 50percent) flushed in dibutyl phthalate are dispersed in a solution of 1.8parts of cellulose nitrate (N-content 10.92 percent) in a mixture of 9.3parts of cyclohexanone and 3.4 parts of dibutyl phthalate. Thesuspension is heated to 100 C. and it is emulsified in 50 parts of a 20percent solution of sodium chloride in water at 70 C. After cooling to50 C., 50 parts by volume ofa 14 percent solution of sodium hydrogensulphide in water are added to the emulsion and the mixture ismaintained at 40 C. while stirring for 45 minutes. The capsules thusformed contain all the Milori blue in the wall. The size of the capsulesis 20-80 2.

EXAMPLE X Into a solution of 1 part of a color forming compound and 25parts of cellulose acetobutyrate (13 percent acetyl content, 37 percentbutyryl content) in a mixture of 49 parts of cyclohexanone and 25 partsof chlorinated paraffin, 94 parts of fine zinc sulphide are suspended.The suspension is heated to 80 C. and dispersed in 323 parts of a 9.3percent aqueous sodium chloride solution, whereafter the emulsionobtained is incorporated by stirring into 275 parts of an 18 percentaqueous solution of sodium hydroxide. After a reaction time of 15minutes at 70 C., the entire quantity of cellulose acetobutyrate whichhad been present in the droplets of the emulsion is converted intocellulose, capsules having formed, in the .walls of which, consisting ofcellulose, the entire quantity of zinc sulphide is contained.Consequently, 750 percent of zinc sulphide have been incorporated intosaid wall. The size of the capsules is 5 to 10 ;.L.

For better illustration of the process according to the invention,reference is made to the diagrammatic graphic representation which isself-explanatory.

1n the following a few examples are given for preparing color reactionpapers with a material produced according to the process of thisinvention containing microcapsules, and for incorporating this materialinto paper pulp which is worked up in the production of color reactionpapers, as known per se.

EXAMPLE X1 10 parts of cellulose capsules (diameter about 1020 1), whichcontain in their walls 133 percent of zinc sulphide, based on the weightof the cellulose, and of which the content consists of a 4 percentsolution of a mixture of 1 part of N- benzoyl leucomethylene blue and 3parts of 3-methyl spirodinaphthopyran in liquid chlorinated paraffin,are suspended in a trituration of 12 parts of clay, which is treatedwith a strong acid, with 78 parts of a 7 percent solution of polyvinylalcohol in water. Using the coating composition obtained in this manner,a white paper of 40 g./m. is coated in known manner with an applicationof 50 g./m. After drying, a pressure-sensitive self-writing" colorreaction paper is obtained which supplies a blue record.

EXAMPLE Xll 24 parts of paper pulp (cellulose content 5 percent) aremixed with 1 part of cellulose capsules (wall 320 percent zinc sulphide,based on cellulose, content 4 percent solution of 3-methyl-spirodinaphthopyran in liquid chlorinated paraffin) and 4 partsof a trituration of 20 parts of acid clay with 80 parts of water, andsheets of paper are produced from this mixture.

EXAMPLE Xlll 12 parts of cellulose capsules (diameter about 10-20 ,u.),in the wall of which are incorporated 750 percent of zinc sulphide,based on the weight of the cellulose, and of which the content consistsof a 4 percent solution of a mixture of 1 part of N-benzoylleucomethylene blue and 3 parts of 3-methyl spirodinaphthopyran inliquid chlorinated paraffin, are suspended in a trituration of 12 partsof clay, which is treated with a strong acid, with 78 parts of a 7percent solution of polyvinyl alcohol in water. With the coatingcomposition obtained in this manner, a white paper of 40 g./m. is coatedin a known manner with an application of 50 g./m.

EXAMPLE XIV 8 parts of microcapsules of denitrated cellulose nitrate, inthe wall of which are incorporated 110 percent of titanium dioxide andthe content of which consists of a 4 percent solution of 3-methylspirodinaphthopyran in diphenoxyethyl formal, are suspended in atrituration of 1 part of a clay treated with acid in 9 parts of a 5percent polyvinyl alcohol solution in water and a white paper of 40g./m. is coated with this coating composition.

EXAMPLE XV 26.4 parts of microcapsules of cellulose, in the wall ofwhich are incorporated 133 percent of zinc sulphide and which contain asolution of 3 parts of 3-methyl spirodinaphthopyran and 1 part ofN-benzoyl leucomethylene blue in 96 parts of liquid chlorinatedparafiin, are suspended in parts of a 3 percent solution of polyvinylalcohol in water. A white paper of about 40 g./m. coated with thiscomposition, represents a transfer sheet which can be used in a knownmanner for duplicating purposes in combination with a sheet carrying acoating which consists of a clay treated with acid.

What is claimed is:

1. A process for the production of microcapsules enclosing liquid and/orsolid substances which comprises converting into a polymeric insolublereaction product a film-forming compound consisting of a cellulose esterof an organic acid dissolved in the dispersed phase of a liquiddispersion system which contains dissolved in its continuous phasesodium hydroxide that reacts with said cellulose ester in solution undersaponification to give a polymeric insoluble reaction product, andincorporating particles of finely divided solid substances selected fromthe group consisting of titanium dioxide, zinc sulphide, a mixture ofthe two, tertiary calcium phosphate, barium sulphate, zinc oxide, amixture of titanium dioxide and calcium carbonate and carbon black, intothe walls of said microcapsules during their formation in amounts fromabout 100 percent up to 750 percent calculated on the organic part ofthe capsule walls, thereby increasing the resistance of the walls tomechanical stress so as to positively exclude damaging of the wallsduring processing and storage.

2. A process for the production of microcapsules enclosing liquid and/orsolid substances which comprises converting into a polymeric insolublereaction product a film-forming compound consisting of cellulose nitratedissolved in the dispersed phase of a liquid dispersion system whichcontains dissolved in its continuous phase sodium hydrogen sulphide thatreacts with said cellulose nitrate in solution under denitration to givea polymeric insoluble reaction product, and incorporating particles offinely divided solid substances selected from the group consisting oftitanium dioxide, zinc sulphide, a mixture of the two, tertiary calciumphosphate, barium sulphate, zinc oxide, a mixture of titanium dioxideand calcium carbonate and carbon black into the walls of saidmicrocapsules during their formation in amounts from about percent up to750 percent calculated on the organic part of the capsule walls, therebyincreasing the resistance of the walls to mechanical stress so as topositively exclude damaging of the walls during processing and storage.

2. A process for the production of microcapsules enclosing liquid and/orsolid substances which comprises converting into a polymeric insolublereaction product a film-forming compound consisting of cellulose nitratedissolved in the dispersed phase of a liquid dispersion system whichcontains dissolved in its continuous phase sodium hydrogen sulphide thatreacts with said cellulose nitrate in solution under denitration to givea polymeric insoluble reaction product, and incorporating particles offinely divided solid substances selected from the group consisting oftitanium dioxide, zinc sulphide, a mixture of the two, tertiary calciumphosphate, barium sulphate, zinc oxide, a mixture of titanium dioxideand calcium carbonate and carbon black into the walls of saidmicrocapsules during their formation in amounts from about 100 percentup to 750 percent calculated on the orGanic part of the capsule walls,thereby increasing the resistance of the walls to mechanical stress soas to positively exclude damaging of the walls during processing andstorage.